Institute for Research in Dental Sciences, Faculty of Dentistry, Universidad de Chile, Santiago 8380544, Chile.
Department of Basic Sciences of Health, Faculty of Health Sciences, Pontificia Universidad Javeriana, Cali 760031, Colombia.
Int J Mol Sci. 2022 Aug 21;23(16):9444. doi: 10.3390/ijms23169444.
Muscle and bone are tightly integrated through mechanical and biochemical signals. Osteoclasts are cells mostly related to pathological bone loss; however, they also start physiological bone remodeling. Therefore, osteoclast signals released during bone remodeling could improve both bone and skeletal muscle mass. Extracellular ATP is an autocrine/paracrine signaling molecule released by bone and muscle cells. Then, in the present work, it was hypothesized that ATP is a paracrine mediator released by osteoclasts and leads to skeletal muscle protein synthesis. RAW264.7-derived osteoclasts were co-cultured in Transwell chambers with flexor digitorum brevis (FDB) muscle isolated from adult BalbC mice. The osteoclasts at the upper chamber were mechanically stimulated by controlled culture medium perturbation, resulting in a two-fold increase in protein synthesis in FDB muscle at the lower chamber. Osteoclasts released ATP to the extracellular medium in response to mechanical stimulation, proportional to the magnitude of the stimulus and partly dependent on the P2X receptor. On the other hand, exogenous ATP promoted Akt phosphorylation (S473) in isolated FDB muscle in a time- and concentration-dependent manner. ATP also induced phosphorylation of proteins downstream Akt: mTOR (S2448), p70S6K (T389) and 4E-BP1 (T37/46). Exogenous ATP increased the protein synthesis rate in FDB muscle 2.2-fold; this effect was blocked by Suramin (general P2X/P2Y antagonist), LY294002 (phosphatidylinositol 3 kinase inhibitor) and Rapamycin (mTOR inhibitor). These blockers, as well as apyrase (ATP metabolizing enzyme), also abolished the induction of FDB protein synthesis evoked by mechanical stimulation of osteoclasts in the co-culture model. Therefore, the present findings suggest that mechanically stimulated osteoclasts release ATP, leading to protein synthesis in isolated FDB muscle, by activating the P2-PI3K-Akt-mTOR pathway. These results open a new area for research and clinical interest in bone-to-muscle crosstalk in adaptive processes related to muscle use/disuse or in musculoskeletal pathologies.
肌肉和骨骼通过机械和生化信号紧密结合。破骨细胞主要与病理性骨丢失有关，但它们也启动生理性骨重塑。因此，骨重塑过程中破骨细胞释放的信号可以改善骨和骨骼肌质量。细胞外 ATP 是一种由骨细胞和肌肉细胞释放的自分泌/旁分泌信号分子。在本研究中，假设 ATP 是一种由破骨细胞释放的旁分泌介体，可导致骨骼肌蛋白合成。RAW264.7 衍生的破骨细胞与从小鼠屈趾短肌（FDB）中分离的 FDB 肌肉在 Transwell 室中共培养。在上室中的破骨细胞通过控制培养基扰动进行机械刺激，导致下室中 FDB 肌肉的蛋白合成增加一倍。破骨细胞在机械刺激下向细胞外介质中释放 ATP，与刺激的幅度成正比，部分依赖于 P2X 受体。另一方面，外源性 ATP 以时间和浓度依赖的方式促进分离的 FDB 肌肉中 Akt 的磷酸化（S473）。ATP 还诱导 Akt 下游蛋白的磷酸化：mTOR（S2448）、p70S6K（T389）和 4E-BP1（T37/46）。外源性 ATP 使 FDB 肌肉的蛋白质合成率增加 2.2 倍；这种作用被苏拉明（通用 P2X/P2Y 拮抗剂）、LY294002（PI3K 抑制剂）和雷帕霉素（mTOR 抑制剂）阻断。这些阻滞剂以及 apyrase（ATP 代谢酶）也消除了共培养模型中破骨细胞机械刺激引起的 FDB 蛋白合成的诱导。因此，本研究结果表明，机械刺激的破骨细胞通过激活 P2-PI3K-Akt-mTOR 途径释放 ATP，导致分离的 FDB 肌肉中的蛋白质合成。这些结果为与肌肉使用/废用或肌肉骨骼病理学相关的适应性过程中的骨-肌肉串扰的研究和临床兴趣开辟了一个新领域。
